Effect of different types of regular exercise on physical fitness in adults with overweight or obesity: Systematic review and meta‐analyses

Summary This systematic review examined the effect of exercise training interventions on physical fitness in adults with overweight or obesity and compared the effectiveness of different types of exercise training. Four electronic databases were searched. Articles were included if they described randomized controlled trials of exercise training interventions and their effect on maximal oxygen consumption or muscle strength in adults with overweight or obesity. Changes in outcome parameters were analyzed using random effects meta‐analyses for different training types (aerobic, resistance, combined aerobic plus resistance, and high‐intensity interval training). Eighty‐eight articles satisfied the inclusion criteria of which 66 (3964 participants) could be included in the meta‐analyses. All training types increased VO2max (mean difference 3.82 ml/min/kg (95% CI 3.17, 4.48), P < 0.00001; I 2 = 48%). In direct comparisons, resistance training was less effective in improving VO2max than aerobic training, HIIT was slightly more effective than aerobic training, and no difference between aerobic and combined aerobic plus resistance training was found. For muscle strength benefits, incorporation of resistance exercise in the training program is indicated. Exercise training increases VO2max and muscle strength in adults with overweight or obesity. Differences between training types should be weighed with other needs and preferences when health professionals advise on exercise training to improve physical fitness.

meta-analyses. All training types increased VO 2max (mean difference 3.82 ml/min/kg (95% CI 3.17, 4.48), P < 0.00001; I 2 = 48%). In direct comparisons, resistance training was less effective in improving VO 2max than aerobic training, HIIT was slightly more effective than aerobic training, and no difference between aerobic and combined aerobic plus resistance training was found. For muscle strength benefits, incorporation of resistance exercise in the training program is indicated. Exercise training increases VO 2max and muscle strength in adults with overweight or obesity. Differences between training types should be weighed with other needs and preferences when health professionals advise on exercise training to improve physical fitness. In the general population, regular exercise is well-known to have beneficial effects on physical fitness, such as an increase in aerobic capacity and increased muscle strength, which are important for the ability to lead a physically active life and for health. 1 In order to define the role of regular exercise in the management of adults with overweight or obesity, it is important to know what the effects on physical fitness are in this specific group of individuals. In general, physical fitness (per kg body weight) is lower in individuals with than in those without overweight or obesity. 2,3 We therefore started with a literature search of systematic reviews on this topic that were published over the last 10 years (2009-2019). This resulted in six reviews. [4][5][6][7][8][9] Miller et al. 4  Batacan et al. 6 focused on the effects of high intensity interval training (HIIT). Sixty-five studies with different study designs in populations with normal weight and overweight were included. The inclusion criteria were not strict: in many studies categorized as studies in individuals with overweight or obesity, this was not mentioned as one of the inclusion criteria in the original study. The authors concluded that short (<12 weeks) and long-term (≥12 weeks) HIIT improve VO 2max in individuals with overweight or obesity as well as in individuals in the non-overweight group.
Türk et al. 8 compared the effects of high intensity (continuous and interval) exercise and lower intensity endurance exercise or no exercise on VO 2max . Fifteen studies were included. The conclusion of the authors was that high intensity exercise was superior to improve cardiopulmonary fitness in comparison with lower intensity or no exercise in adults with obesity. Su et al. 9 compared the effects of HIIT with those of moderate intensity continuous training (MICT). Sixteen studies were included. Overall HIIT was equally effective as MICT in improving VO 2max , but HIIT training with longer (≥2 min) intervals appeared to be more effective than MICT. Hita-Contreras et al. 7 reviewed the effects of exercise interventions on muscle strength and gait speed in sarcopenic obesity. Five RCT's were included, two of which used electrostimulation as exercise intervention. The authors concluded that exercise increases grip strength and gait speed in people with sarcopenic obesity. The effects of different types of training were not analyzed.
Because of the limited information available from these systematic reviews, which mostly focused on specific groups, did not distinguish between types of training or studied the combination with a weight loss diet, we decided to do a systematic review and metaanalyses on the topic in the context of the EASO Physical Activity Working Group guidelines development. The aim of this systematic review was to examine the impact of various types of exercise interventions (aerobic training, resistance training, combined aerobic and resistance training, and high-intensity interval training) on physical fitness, with a focus on cardiorespiratory fitness and muscle strength, in adults with overweight or obesity and compare their effectiveness.
A secondary aim was to compare the effectiveness in adults with normal weight and those with overweight or obesity.  Table S1. Reference lists from the resulting articles were screened to identify additional articles.

| Study selection, inclusion, and exclusion
Articles were included if the RCT involved adults (>18 years, no maximum age) with overweight (BMI ≥ 25 kg/m 2 ) or obesity (BMI ≥ 30 kg/m 2 ) participating in physical activity interventions, that is, exercise training programs, or interventions promoting increases in physical activity. Studies focusing on the primary prevention of weight gain/obesity were not included. The presence of obesity comorbidities, such as type 2 diabetes, hypertension, dyslipidemia, metabolic syndrome, liver disease (NAFLD/NASH), and osteoarthritis, was not an exclusion criterion. Exercise training programs included regular sessions with one or more types of exercise (aerobic and/or resistance and/or high-intensity interval training). Exercise sessions could be supervised, partially supervised or non-supervised. Exercise interventions in combination with other interventions (e.g., diet) were excluded. Comparators included no intervention, another form of exercise or sham exercise (e.g., stretching).
Abstracts and full texts were assessed for eligibility independently by two authors (M. A. v. B. and A. P.) with uncertainty regarding eligibility discussed among authors.

| Data extraction
Data were extracted by two authors using standardized forms. The following characteristics were extracted: reference, study design, number of participants included in intervention and control groups, population characteristics (age, BMI, %female, comorbidities for intervention, and control groups), description of intervention (program duration, number of sessions per week, type of training/topic, and supervision/delivery) and comparison, and outcomes. Additional data were obtained from six authors. [10][11][12][13][14][15] The findings pertaining to cardiorespiratory fitness (measured or estimated VO 2max ), muscle strength, and any other parameter of physical function of each included article are reported.

| Data synthesis and statistical analysis
To calculate the effect size of each study, we used the mean change (post-to pre-intervention) and SD of the variable of interest over the experimental period in the control and intervention groups. If these values were not reported, we calculated the mean difference as the difference in mean pre and post intervention and its SD using the formula: SD = square root ((SD pretreatment ) 2 + (SD posttreatment ) 2 ) − (2r × SD pretreatment × SD posttreatment )). Because the pretest-posttest correlation coefficients (r) were not reported in the studies, a conservative r value of 0.5 was assumed throughout. If an exact p value for the within group intervention effect was reported, we used this value together with the subject number (N) to estimate the SD of the effect.
The meta-analysis of included studies was conducted using the Cochrane Review Manager 5.3 software. 16 If a study included more than two experimental groups, which were compared with one control group, the number of subjects in the control group was divided by the number of comparisons. The effect size was expressed as mean difference (MD) or standardized mean difference (SMD) when not all studies reported the outcome in the same units. Most studies reported data from a completers analysis. In a limited number of studies intention-to-treat analysis was performed and, if available, these results were included in the meta-analyses.
Random-effects models were used for the statistical analysis. The effect size is reported as the (standardized) mean difference with its 95% confidence interval (95% CI). Effect sizes were considered large, medium, small and negligible when SMD was >0.8, between 0.5 and 0.8, between 0.2 and 0.5 and below 0.2, respectively. 17 Heterogeneity was measured using the I 2 test. 18 Heterogeneity was considered low, moderate, and high when I 2 was <50%, between 50 and 75% and ≥75%. 19

| Quality assessment
Study quality was assessed with a standardized tool including 14 criteria, as previously described. 20 Study quality was defined as good, fair, or poor when 0, 1, or ≥2 criteria defined as "fatal flaws" (randomization, dropout <20%, intention-to-treat analysis) were not fulfilled. Quality assessment was conducted independently by two reviewers (M. A. v. B. and A. P.) using this standardized tool. Any disagreement between the reviewers was resolved through discussion.

| Risk of bias assessment
Publication bias was assessed by visual inspection of the funnel plots.
When the funnel plot showed signs of asymmetry and the number of included studies was >10, Egger's test was performed.

| RESULTS
The database search yielded 3068 articles, 2831 of which were eliminated based on titles and abstracts alone. Twenty-five studies were added from additional sources. Full texts were retrieved from 162 articles and 88 satisfied the inclusion criteria ( Figure S1). Of these, 66 could be included in the various meta-analyses. The 66 studies included 3954 participants, sample size ranged from 12 to 464 (median 43), training duration ranged from 2 to 70 weeks (median 12 weeks), van BAAK ET AL. % females participating in the studies ranged from 0 to 100% (median 82%), mean age in study groups ranged between 20 and 75 years (median 46 y), mean baseline BMI ranged between 26.4 and 37.2 kg/m 2 (median 30.9) and mean baseline VO 2max ranged between 14.9 and 39.7 ml/min/kg (median 28.4). The quality assessment yielded 21 studies that were of good quality, 28 of fair and 17 of poor quality, mainly due to high dropout rates and lack of an intention-to-treat analysis (Table S2). Table 1 summarizes the effects of different types of exercise training on selected physical fitness parameters in adults with overweight or obesity.

| Effect of exercise training on cardiorespiratory fitness
For the meta-analyses on cardiorespiratory fitness the outcome was maximal or peak oxygen consumption (VO 2max ). Only studies which expressed VO 2max in ml/min/kg were included to take the effect of potential weight changes during the intervention period into account.

| Effect of aerobic exercise training on cardiorespiratory fitness
The characteristics of the 24 included RCTs 10,11,14,21-41 with 1802 participants are presented in Table S3. The meta-analysis had 41 study arms with 995 individuals in the experimental groups and 447 in the control groups. It showed that aerobic exercise training significantly improved VO 2max (mean difference (MD) 4.08 ml/min/kg (95% CI 3.22, 4.95), P < 0.00001). The heterogeneity was moderate (I 2 = 61%).
The funnel plot looked asymmetric, which was confirmed by Egger's test (P = 0.001) ( Figure S3). When the study by Church et al. 24 was excluded, Egger's test was no longer significant (P = 0.084). The T A B L E 1 Summary of meta-analyses on the effects of different types of exercise training (aerobic, resistance, combined aerobic plus resistance, and high-intensity interval training) on VO 2max , muscle strength and other fitness parameters in adults with overweight or obesity The heterogeneity was moderate (I 2 = 59%) ( Figure S4).
The effect size was large (SMD 0.81 (95% CI 0.22, 1.41)). Quality assessment of the studies included in this meta-analysis showed that all studies except one 33 were of fair or good quality (Table S2).

| Effect of combined aerobic plus resistance exercise training on cardiorespiratory fitness
The characteristics of the seven included RCTs 12,14,29,44-47 with 377 participants are presented in Table S5. Seven study arms were included with 165 individuals in the experimental groups and 153 in the control groups. The meta-analysis showed that combined aerobic plus resistance training significantly improved VO 2max (MD 4.57 ml/ min/kg (95% CI 2.14, 7.00), P = 0.0002). The effect size was medium (SMD 0.78 (95% CI 0.40, 1.16)). The heterogeneity was also large (I 2 = 74%), which was due to the study by Hara et al. 45 When this study was excluded the MD was reduced to 2.95 ml/min/kg (95% CI 2.05, 3.85), P < 0.00001, I 2 = 0%. The forest plot is shown in Figure S6. The majority of the studies included in this meta-analysis was of fair-to-good quality, only one had poor quality 47 (Table S2).
Excluding this poor-quality study resulted in an MD of 4.98 ml/min/ kg (95% CI 2.07, 7.88), P = 0.0008, I 2 = 78%. The funnel plot looked asymmetric due to the study by Hara et al. 45 ( Figure S7) The effect size was large (SMD 0.84 (95% CI 0.57, 1.11)). The forest plot is shown in Figure S8. Two studies 50 Figure S9) showed some evidence of asymmetry, but Egger's test was not significant (P = 0.222).

| Comparison of the effect of different types of training on cardiorespiratory fitness
We also analyzed whether a certain training type(s) should be preferred as training regimen for the improvement of VO 2max in adult with overweight or obesity. The number of studies that compared certain types of training is limited. We were able to analyze the comparison of aerobic endurance type training with resistance training, with combined aerobic and resistance training and with HIIT.

Aerobic training versus resistance training
The characteristics of the eight included RCTs 13-15,21,29,33,53,54 with a total of 322 participants are presented in Table S7. Eight study arms were included with 143 individuals in the resistance training groups and 137 in the aerobic training groups. The meta-analysis showed that aerobic training improved VO 2max more than resistance training (MD −1.40 ml/min/kg (95% CI −2.41, −0.38, P = 0.007) ( Figure S10).
The effect size was small (SMD −0.37 (95% CI −0.63, −0.12)). The heterogeneity was low (I 2 = 11%). Quality assessment of the studies showed that five of the studies had fair or good quality, whereas three were of poor quality 15,33,53 (Table S2) Figure S12). The SMD was 0.07 (95% CI −0.22, 0.35)). The heterogeneity was low (I 2 = 0%). Quality assessment of the studies included in the meta-analysis showed that three of the studies had fair or good quality, whereas one was of poor quality 15 (Table S2)

| Effect of exercise training on muscle strength
For the meta-analyses on muscle strength various outcomes were used, including static or dynamic muscle strength of different muscle groups. When available, strength parameters expressed per kg body weight or muscle mass were included to take the effect of potential weight changes during the intervention period into account. The outcomes of the meta-analyses are reported as standardized mean differences (SMD), because study outcomes (strength measurements and units of measurement) differed across studies.

| Effect of aerobic exercise training on muscle strength
The characteristics of the six included RCTs 14,23,33,37,70,71 with a total of 206 participants are presented in Table S10. Twelve study arms were included with 78 individuals in the aerobic exercise groups and 76 in the no exercise control groups. The meta-analysis showed no significant difference in effect (SMD 0.26 (95% CI −0.06, 0.58), P = 0.12). The heterogeneity was low (I 2 = 0%) ( Figure S16). Quality assessment of the studies included in the meta-analysis showed that two of the six studies had poor quality 33,70 (Table S2). Removing the poor-quality studies from the meta-analysis resulted in a SMD of 0.08 (95% CI −0.41, 0.57), P = 0.75, I 2 = 0%, N = 66). Visual inspection of the funnel plot ( Figure S17) did not suggest asymmetry.

| Effect of resistance exercise training on muscle strength
The characteristics of the 12 included RCTs 14,33,42,70-78 with 612 participants are presented in Table S11. Thirty-two study arms were included with 291 individuals in the resistance exercise groups and 206 in the no exercise control groups. The meta-analysis showed a significant difference in effect in favor of resistance training (SMD 0.74 (95% CI 0.54, 0.93), P < 0.00001). The heterogeneity was low (I 2 = 0%) ( Figure S18). Quality assessment of the studies included in the meta-analysis showed that four of the 12 studies had poor quality 33,70,71,77 (Table S2). Removing the poor-quality studies from the meta-analysis resulted in a SMD of 0.76 (95% CI 0.53, 0.98), P < 0.00001, I 2 = 0%, N = 379). The funnel plot ( Figure S19) showed no evidence of asymmetry (Egger's test P = 0.698).

| Effect of combined aerobic and resistance exercise training on muscle strength
The characteristics of the six included RCTs 14,46,47,70,79,80 with a total of 218 participants are presented in Table S12. Thirteen study arms were included with 74 individuals in the aerobic plus resistance exercise groups and 71 in the no exercise control groups. The metaanalysis also showed a significant difference in effect (standardized mean difference (SMD) 0.62 (95% CI 0.27, 0.96), P = 0.0004). The heterogeneity was low (I 2 = 0%) ( Figure S20). Quality assessment of the studies included in the meta-analysis showed that two of the six studies had poor quality 47,70 (Table S2). Removing the poor-quality studies from the meta-analysis resulted in a SMD of 0.67 (95% CI 0.24, 1.10), P = 0.002, I 2 = 0%, N = 93). Visual inspection of the funnel plot did not suggest serious asymmetry ( Figure S21).

| Effect of high-intensity interval training on muscle strength
There were no studies that investigated the effect of HIIT on muscle strength in comparison to no exercise training.

| Comparison of the effect of different types of training on muscle strength
Resistance training versus aerobic training The characteristics of the seven included RCTs 13,33,53,70,71,81 with 251 participants are presented in Table S13.

Resistance training versus HIIT
No studies.

| Effect of exercise training on muscle strength in individuals with or without overweight or obesity
Four studies 68,77,82,83 were found that directly compared the effects of exercise training on muscle strength in individuals with normal weight and with overweight or obesity. Pescatello et al. 82 and Vincent et al. 77 studied the effects of resistance training and found no difference in the strength response between the group with normal weight and that with overweight or obesity. On the other hand, no differences in the strength or flexibility response to combined aerobic and resistance exercise training were found by Blake et al. 68 Gondim et al. 69 reported an increase in muscle strength in the group with obesity, but not in the group with normal weight, however whether there was a significant difference between the groups was not reported.

| Exercise training and other physical fitness parameters
Six studies 46,72,73,76,79,80 reporting the effect of resistance or combined aerobic and resistance exercise training on muscle strength also provided data on the effects on other parameters of physical fitness, such as flexibility, balance, global physical capacity score, walking speed.
The meta-analysis ( Figure S24) showed that resistance training and combined aerobic plus resistance exercise training had a positive effect on these parameters (SMD 0.66 (95% CI 0.37, 0.95), P < 0.00001). Heterogeneity was low (I 2 = 0%). Visual inspection of the funnel plot ( Figure S25) did not suggest asymmetry.
Three studies 23,37,38 reported on the effect of aerobic training on flexibility. Two 23,37 found an improvement, one no effect. 38 Manini et al. 83

| DISCUSSION
In this systematic review and series of meta-analyses we tried to determine the effect of different training modalities on cardiorespiratory fitness and muscle strength in individuals with overweight or obesity. Additionally, we investigated the effects on other parameters of physical fitness (e.g., overall score, flexibility, balance, walking speed). We also tried to evaluate whether the responses were similar in groups with normal weight and groups with overweight or obesity. In general, this systematic review and the included meta-analyses confirm the results of previous ones examining the effects of exercise training on physical fitness in (subgroups of) adults with overweight or obesity, 4-9 but extends these by using more strict inclusion criteria and a more detailed comparison among training modalities. Aerobic training, as expected, increased VO 2max as did combined aerobic plus resistance training. Whether resistance training also improves VO 2max is a topic of discussion in the literature. 84,85 We found that resistance training was also effective, although less than aerobic training, in increasing VO 2max , which may be related to the relatively low level of baseline VO 2max in the population with overweight or obesity. 84 The majority of studies in this review were in line with general recommendations for aerobic and resistance exercise for the improvement or maintenance of physical fitness (e.g., that of the American College of Sports Medicine 86 ), although the combination of the two, which is recommended in most guidelines, was studied less frequently. We found that combined aerobic and resistance exercise was equally effective as aerobic training in improving VO 2max , whereas aerobic plus resistance training was equally effective as resistance training for muscle strength, although this latter conclusion was based on only three studies.
Studies included males and females with a wide range of mean ages (18-75 years), BMIs (26.4-40.5 kg/m 2 ) and initial fitness levels (VO 2max 14.9-39.5 ml/min/kg) and therefore appear to cover the overall adult population with overweight or obesity, except for the morbid obesity category. Nevertheless, not all training modalities were studied in the same populations. For instance, participants in the high-intensity training studies were generally younger, whereas those participating in training studies where muscle strength was the outcome were on average older and had lower BMIs.
Intervention durations ranged between 2 and 70 weeks. There was some evidence that very short (2-4 weeks) and very long durations (>26 weeks) were associated with less pronounced training effects, which may be related with the time course of obtaining the optimal training effect: in short studies the optimal effect may not have been attained yet, whereas in longer duration interventions reduced compliance may play a role in diminishing the training effect.
In conclusion, in individuals with overweight or obesity all training modalities included in this review (aerobic, resistance, combined aerobic and resistance and high-intensity interval training) increased VO 2max .
HIIT and exercise programs that included aerobic training were the most effective. For muscle strength benefits, incorporation of resistance exercise in the training program is required. Health professionals should weigh these differences with the needs and preferences of the individual with overweight or obesity when advising on exercise.